In electronic devices electronic circuits may be equipped with current collectors of a type such as in electrochemical or electro-optical devices. For example an electrochemical device is a battery such as a rechargeable Li-ion solid-state battery having current collector of non-planar design. Another example of an electro-optical device is a light collector wherein current from a photovoltaic reaction is collected in a 3D electrode. Batteries are electrochemical cells which store and supply electrical energy as a product of a chemical reaction or conversely, light is generated.
Thin-film battery structures of known type are disclosed e.g. in WO2010032159, the contents of which are included by reference, wherein for example all-solid state compositions are deposited on 3D micro-patterned structures. In this respect, where early battery structures utilize liquid electrolytes, all-solid state compositions utilize electrolytes of a solid state type, which are inherently safer in use. In these structures a large variety of materials are and have been used for the respective electrodes for example as disclosed in US 20110117417. In discharging battery mode, the anode is the “negative electrode” to which the positive current flows, from the cathode, being the “positive electrode”. During charge these functions are reversed. Irrespective charging mode, the electrochemical relationship may be characterized by charge exchange between a negative electrode material and a positive electrode material, the negative electrode material having a workfunction or redox potential that is lower than the workfunction or redox potential of the positive electrode material.
For example, known negative electrode (anode) materials are Li4Ti6O12 (Titanate); LiC6 (Graphite); Li4.4 Si (Silicon) and Li4.4Ge (Germanium) known positive electrode (cathode) materials are LiCOO2 (LCO), LiCoPO4, (doped) LiMn2O4 (LMO), LiMnPO4, LiFePO4 (LFP), LiFePO4F(LFPF) or LiCO1/3Ni1/3Mn1/3O2 (LCNMO).
Known (solid state) electrolytes might include lithium iodide (LiI), lithium phosphate (Li3PO4) and lithium phosphorus oxynitride (LiPON). In addition, lithium salts, such as LiPF6, LiBF4 or LiClO4 in an organic solvent, such as ethylene carbonate, dimethyl carbonate, diethyl carbonate, propylene carbonate are known to have a typical conductivity of about 10 mS/cm at RT. The solvent decomposes on initial charging and forms a solid layer called the solid electrolyte interphase (SEI).
Solid polymer separators may also be included, such polymers having transport capacity often due to having a lithium salt disposed therein as known in the state of the art. Work has also been performed with lithium and halide materials, particularly, in some examples, a lithium aluminum tetrahalide such as lithium aluminum tetrafluoride (LiAlF4).
Similarly, in a photovoltaic device, a conformal functional coating may be provided on the current collector, that aids in conversion of light to electric power or vice versa.
In the referenced type, a high specific surface area of current collector structures i.e. electrodes enable high currents to be drawn from these batteries. Moreover, they also will enable quick charging of these batteries. In the known device high-aspect ratio structures such as pillars, trenches or holes are etched in a silicon wafer. In order to make the fabrication of these batteries cost-effective, a desire exists to produce these on cheaper substrates (e.g. metal/plastic foils) with a cheaper large-area process.
Once such structures are made on a bendable metal foil, they can be manufactured in large-scale processes, e.g. a roll-to-roll process where the following can be done: 1) Coiling, winding or stacking it to increase the energy or power density per unit volume. 2) Integrating it on flexible devices like flexible displays, signage etc.
Although, high-aspect ratio structures can be made in nanometer scale the height or depth of these high-aspect ratio structures need to be in the microns range for delivering enough charge capacity for the battery. The reason pillar structures are preferred is due to the easy accessibility of their entire surface when compared to porous or perforated structures of similar aspect ratio and dimensions. In the prior art many methods to produce these are non-economical (e.g. involving silicon microfabrication and long-time electrodeposition). Moreover, to do any of these, the design of the stack is in need for optimization because otherwise while winding or flexing, the pillar structure could be damaged inhibiting proper electrochemical action of the device.
A need still exists to produce these high-aspect ratio structures in a simple and reliable way.